title: Time-resolved infrared studies of a trimethylphosphine model derivative of [FeFe]-hydrogenase.
abstract: Model compounds that structurally mimic the hydrogen-producing active site of [FeFe]-hydrogenases have been studied to explore potential ground-state electronic structure effects on reaction mechanisms compared to hexacarbonyl derivatives. The time-dependent behavior of Fe2(μ-S2C3H6)(CO)4(PMe)2 (A) in room temperature n-heptane and acetonitrile solutions was examined using various ultrafast UV and visible excitation pulses with broadband IR-probe spectroscopy of the carbonyl (CO) stretching region. Ground- and excited-state electronic and CO-stretching mode vibrational properties of the possible isomers of A were also examined using density functional theory (DFT) computations. In n-heptane, 355 and 532 nm excitation resulted in short-lived (135 ± 74 ps) bands assigned to excited-state, CO-loss photoproducts. These bands decay away, forming new long-lived absorptions that are likely a mixture of isomers of both three-CO and four-CO ground-state isomers. These new bands grow in with a time scale of 214 ± 119 ps and persist for more than 100 ns. In acetonitrile, similar results are seen with a 532 nm pump, but the 355 nm data lack evidence of the longer-lived bands. In either solvent, the 266 nm pump data seem to also lack longer-lived bands, but the intensities are significantly lower in this data, making firm conclusions more difficult. We suggest that these wavelength-dependent excitation dynamics significantly alter potential mechanisms and efficiencies for light-driven catalysis.
authors.affiliation: Department of Chemistry and Physics, Hood College , 401 Rosemont Avenue, Frederick, Maryland 21701-8524 United States.
authors.forename: Melissa
authors.initials: M
authors.lastname: Johnson
authors.forename: James
authors.initials: J
authors.lastname: Thuman
authors.forename: Roger G
authors.initials: RG
authors.lastname: Letterman
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Stromberg
authors.forename: Charles Edwin
authors.initials: CE
authors.lastname: Webster
authors.forename: Edwin J
authors.initials: EJ
authors.lastname: Heilweil
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D055162:Biocatalysis; D006536:Heptanes / Q000737:chemistry; D006864:Hydrogenase / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D007536:Isomerism; D008958:Models, Molecular; D010720:Phosphines / Q000737:chemistry / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D000097:Acetonitriles; D006536:Heptanes; D007506:Iron-Sulfur Proteins; D010720:Phosphines; C028618:n-heptane; C049750:trimethyl phosphine; C118830:iron hydrogenase; D006864:Hydrogenase; C032159:acetonitrile